The present invention pertains to systems and methods for reducing the agglomeration of copper deposited by physical vapor deposition. More specifically, the invention pertains to systems and methods for depositing copper seed layers on a semiconductor wafer. The invention involves the use of an anti-agglomeration agent, so that the copper deposition is completed in an even, continuous and conformal manner.
Integrated circuit (IC) manufacturers have traditionally used aluminum and aluminum alloys, among other metals, as the conductive metal for integrated circuits. While copper has a greater conductivity than aluminum, it has not been used because of certain challenges it presents, including the fact that it readily diffuses into silicon oxide and degrades insulating electrical properties at very low doping concentrations. Recently, however, IC manufacturers have been turning to copper because of its high conductivity and electromigration resistance, among other desirable properties. Most notable among the IC metalization processes that use copper is Damascene processing.
Damascene processing is a method for forming metal lines on integrated circuits. It involves formation of inlaid metal lines in trenches and vias formed in a dielectric layer (inter-metal dielectric). A barrier layer that blocks diffusion of copper atoms is typically formed over the dielectric layer and underneath the metalization. Damascene processing is often a preferred method because it requires fewer processing steps than other methods and offers a higher yield. It is also particularly well-suited to metals such as Cu that cannot readily be patterned by plasma etching.
In a typical copper IC process, the formation of the desired conductive wires on the chip generally begins with a seed layer, usually deposited by physical vapor deposition (PVD). The seed layer provides a conformal, conductive layer on which a thicker layer of copper is electrofilled in order to fill in the features (e.g., trenches and vias) of the semiconductor wafer. One of the most significant problems with PVD deposition of copper is that the copper tends to agglomerate at the surface. Because of this agglomeration, the copper does not cover the surface in a conformal manner. Coverage that is not conformal means coverage that is uneven; i.e., thicker in some places than others, and that may include actual gaps. Thus the seed layer does not provide a uniform layer for electroplating, which leads to defects in the electroplated copper.
What is needed therefore is an improved process in which copper seed layers are formed with reduced agglomeration.
The present invention pertains to systems and methods for reducing the agglomeration of copper deposited by physical vapor deposition. More specifically, the invention pertains to systems and methods for depositing the copper seed layer on a semiconductor wafer on the barrier layer. The deposition is carried out in a manner that reduces the kinetics of agglomeration (and sometimes the thermodynamic driving force for agglomeration), so that the deposition is completed in an even, conformal manner.
One aspect of the invention provides for a method for physical vapor deposition of copper to form part or all of a seed layer on an integrated circuit surface substrate. The method includes applying a nitrogen-containing agent to incorporate nitrogen into the seed layer to reduce agglomeration of the copper seed layer. The method may employ a hollow-cathode magnetron to deposit the copper. Regardless of the reactor chosen, the method employs a nitrogen-containing gas or plasma. A separate annealing operation may or may not be carried out on the copper seed layer. The nitrogen can be introduced during PVD deposition of the copper. Only a portion of the copper seed layer need contain nitrogen. No actual Cu3N compound need be formed. The method may be used in Damascene processing and dual Damascene processing. The nitrogen-containing agent may be N2, NH3, or NH4OH.
Another aspect of the invention provides for a method for physical vapor deposition of copper to form part or all of a seed layer on an integrated circuit surface substrate. The method includes applying an anti-agglomeration agent to the agent into the seed layer to reduce agglomeration of the copper seed layer. The anti-agglomeration agent may reduce the mobility of the copper in the copper seed layer. The anti-agglomeration agent may contain a metallic element such as silicon or platinum. The method may employ a hollow-cathode magnetron to deposit the copper. Regardless of the reactor chosen, the method preferentially employs a gas or plasma to apply the anti-agglomeration agent. No separate annealing operation need be carried out on the copper seed layer. The anti-agglomeration agent can be introduced during PVD deposition of the copper. Only a portion of the copper seed layer need contain the anti-agglomeration agent. The method may be used in Damascene processing and dual Damascene processing. The anti-agglomeration agent may be a silicon or platinum containing gas.
Another aspect of the invention provides for an apparatus module for physical vapor deposition of copper seed layer on an integrated circuit substrate in a manner that reduces agglomeration of the copper seed layer, including a PVD chamber, a hollow-cathode magnetron, a copper target, a source of a neutral sputtering gas and a source of an anti-agglomeration agent. The anti-agglomeration agent may be a nitrogen, silicon or platinum containing agent. The anti-agglomeration agent source may be a gas or plasma. The apparatus is used to form part or all of a copper layer seed in a manner that reduces agglomeration of the copper. The apparatus may be used in Damascene or dual Damascene processing.
These and other features and advantages of the present invention will be described in more detail below with reference to the associated drawings.